In vitro inhibitory activities of two browse extracts on larval exsheathment of goat nematodes

Nematodes impose a significant economic loss in goat production systems in Ethiopia. Haemonchus contortus and Trichostrongylus colubriformis are the most prevalent species of nematodes. Control using synthetic anthelimintic drugs is limited due to inaccessibility or high cost and tannin-containing forages could provide a cheap and sustainable alternative. The present study examined anthelmintic properties of two tannin-containing browse against H. contortus and T. colubriformis infective larval stage (L3), and to compare larval susceptibility to extracts. The larval exsheathment inhibition assay was employed where the L3 were exposed to extracts obtained from acetone/water (70:30, v/v) extracted dried leaves of Capparis tomentosa and Dodonea angustifolia. Condensed tannin concentrations were 6.8 and 9.3 Abs550 nm/g DM, respectively as measured by the modified Butanol-HCl-Iron method. The L3 (ca. 1000 L3/ml) were obtained from monospecifically infected donor goats. Treatments included extract doses of 1,200, 600, 300, 150 and 0 (control) μg/ml PBS. The L3 were exposed for 3 h, centrifuged and washed 3 times with PBS. Four replicates from each dose were prepared and artificial exsheathment induced using a 40 μl solution of sodium hypochlorite (2%, w/v) and sodium chloride (16.5%, w/v) diluted in 1:400 or 1:500 PBS. Larval exsheathment was recorded microscopically (200×) at 0, 20, 40, and 60 min. Percentage exsheathment was calculated as the ratio of exsheathed over the total exsheated and ensheated larvae. Percentage exsheathment data were subjected to GLM of SAS. The effective dose that causes 50% L3 exsheathment inhibition (EC50) was calculated using a PoloPlus software. There was a dose dependent effect on exsheathment (P<0.001) across extracts with complete inhibition for 1,200 μg/ml regardless of larval species. Mean EC50 values were 332.9 and 275.8 (H. contortus), and 359.6 and 386.9 μg/ ml (T. colubriformis) with C. tomentosa and D. angustifolia, respectively. The extracts exhibited anthelmintic properties against both nematode species and the mean EC50 values suggested higher susceptibility of H. contortus. Results suggest the possible use of the two browse species for simultaneous control of H. contortus and T. colubriformis.